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Abstract It is now accepted that southern South America was formed from several terranes of diverse origin and evolution. However, a detailed history of the accretionary processes has not been unravelled yet. Palaeomagnetism can play an important role in such an endeavour. Palaeomagnetic constraints on the tectonic evolution of this region in the Proterozoic and Palaeozoic are reviewed and discussed. Data from the Rio de la Plata craton suggest that this block was already attached to most major Gondwana blocks by the end of the Proterozoic and may have formed a single continental mass with Congo-Sao Francisco, West Nile and Arabia throughout most of the Vendian. A large ocean separating these cratons from Amazonia and West Africa, prior to Gondwana assembly, is supported by available palaeomagnetic data. To the west of the Rio de la Plata craton is the Pampia terrane. Despite lack of palaeomagnetic data, geological evidence supports a model of Early Cambrian collision between these blocks. An Early Ordovician magmatic arc, the Famatina-Eastern Puna belt, which had developed on the western margin of the already accreted Pampia terrane, shows a systematic pattern of large clockwise rotation that has been interpreted as representative of the whole terrane. The favoured tectonic model portrays a continental magmatic arc with a back-arc basin to the east that was closed when the terrane rotated. There is little doubt of a Laurentian origin for the Cuyania (Precordillera) terrane, given the amount and diversity of evidence, including palaeomagnetism. The tectonic mechanism for accretion and its timing are still controversial. New palaeomagnetic data from Late Ordovician rocks of Cuyania support the ‘Laurentian plateau’ hypothesis, which suggests that Cuyania was still linked to Laurentia well into the Ordovician. Nevertheless, these new data do not rule out the more generally favoured ‘microcontinent model’ To the west of Cuyania is the Chilenia terrane, separated by a belt of ophiolites of Late Ordovician age. Very little is known about this terrane, although some U–Pb ages and Nd model ages point to a Laurentian origin for its basement. Lack of palaeomagnetic data precludes determining its kinematic evolution. The Arequipa-Antofalla block may actually be a composite terrane. Palaeomagnetic data obtained so far come exclusively from the southern Antofalla block. Recently acquired data in the western Puna of Argentina confirm the originally proposed distribution of Early Palaeozoic palaeomagnetic poles, which, despite several uncertainties, delineate a pattern of significant counterclockwise rotations with a possible anomaly in palaeolatitude for the late Cambrian. The data suggest a major tectonic discontinuity between the Eastern and Western Puna of Argentina in the Early Palaeozoic. Four palaeomagnetic poles of Devonian to Permian age from the North Patagonian Massif are consistent in position and age with the Gondwana apparent polar wander path, suggesting that both continental masses have not experienced major relative displacement since the Devonian. The data do not, however, rule out a restricted separation of Patagonia orthogonal to its northern boundary in the Early or Middle Palaeozoic and subsequent collision in the Late Palaeozoic.

Abstract The Carboniferous-Permian Paganzo succession straddles the Pampeanas, Precordillera, and Chilenia terranes. Late Devonian-Early Carboniferous diastrophism of the Chanic event separated very different early and late Paleozoic histories of basin formation. The Paganzo basin was initiated in the Visean by reactivation of old terrane boundaries. The early Paganzo consisted of a suite of discrete fault-controlled depocenters interpreted as transtensional pull-apart basins linked to right-lateral displacement along major crustal faults. Younger phases of basin formation were characterized by amalgamation of these various depocenters into a single broad basin. The Paganzo succession is divided into four supersequences by major hiatuses. These are the Guandacol, Tupe, and lower and upper Patqula-De la Cuesta supersequences. Each is constructed by stacked unconformity- bounded depositional sequences. These four supersequences record the various stages of basin evolution. The Guandacol sediments were deposited in isolated basins. Fieldwork shows a pattern of rapid subsidence and stacking of coarse alluvial facies along basin-bounding faults. The characteristics of the finer grained strata indicate a periglacial influence. The overlying Tupe supersequence suggests a gradual cessation of fault activity as the various depocenters were yoked together. Tupe stratigraphy onlaps the Guandacol-Tupe unconformity and buries some of the previous interbasin highs. In Patqula-De la Cuesta time, the Paganzo basin had widened to its maximum extent. Significant transgressions are recorded in Tupe (Westphalian–Stephanian) and Patqula-De la Cuesta (Artinskian and Kazanian) stratigraphy. Extensive geochemical studies show that Patquia source rocks are oil prone. Although indications are that the Paganzo basin is prospective, it remains largely untested. Regional studies show that the strike-slip faults that controlled Carboniferous basin development in northwestern Argentina diverge northward where they become involved in the Chaco salient of the Bolivian Andes. The Tupambi-Tarija and Escarpment sequences of Bolivia are broadly contemporaneous with the Guandacol and Tupe stratigraphy of the Paganzo basin. They share similar depositional characteristics typical of rapidly subsiding transtensional basins, including stacked alluvial facies, thick debris flow diamictites, massive soft sediment deformation, and dewatering structures. The Escarpment Formation represents an expansion of the earlier Tupambi-Tarija depocenters and contains an anastomosing drainage system.

The tectonic evolution of the central Andes is depicted through analysis of the 30° to 33°S segment, which encompasses the highest part of the Andean Cordillera. A period of rifting, starting as early as 600 Ma, was a milestone in the evolution of the different tectonic regimes that are responsible for the present geological composition and structure of the Andes. The early Paleozoic was an important period of continental accretion when allochthonous terranes, such as Chilenia, were incorporated onto the western margin of Gondwanaland. The subduction zone was located about 300 km east of the present trench. An early Paleozoic magmatic arc was developed in the western Sierras Pampeanas. Sedimentary facies of that age record a continental margin between Chilenia and the magmatic arc, which is associated with a disrupted ophiolite sequence. The Famatinides orogeny produced the first deformation of the Andes and the uplift of the Protoprecordillera during middle to late Devonian times. The Gondwanides orogeny is characterized by subduction of an oceanic plate beneath a continental margin, with the accretion of minor exotic terranes in the southern part of the Andes. Magmatism, eastward migration of the volcanic front, sedimentation pattern, and deformation defined an evolving orogenic sequence. This is correlated to a varying convergence history linked to variations in the apparent polar wandering path of western Gondwanaland during late Paleozoic-early Mesozoic times. The Patagonides orogeny was also governed by changes in relative plate motions during middle to late Mesozoic times. The paleotectonic history suggests that two orogenic styles were produced: a stage with little compression and back-arc volcanism, and a stage with high compression without volcanism but with important deformation and emplacement of postorogenic granitoids. The Andean orogenic cycle is distinguished by conspicuous segments of the orogen that are controlled by the segmentation of the subducted oceanic Nazca plate related to the subduction of aseismic ridges. But the compressive phases and mountain building are more closely related to changes of plate motion, which affected thousands of kilometers of the continental margin, exceeding the length of any individual segment. The age of the subducted oceanic slab is an important factor that controls the magmatic activity and the presence or absence of retroarc magmatism. The relative influence of each proposed mechanisms varies substantially among the different segments.

Abstract In this classic segment, many tectonic processes, like flat-subduction, terrane accretion and steepening of the subduction, among others, provide a robust framework for their understanding. Five orogenic cycles, with variations in location and type of magmatism, tectonic regimes and development of different accretionary prisms, show a complex evolution. Accretion of a continental terrane in the Pampean cycle exhumed lower to middle crust in Early Cambrian. The Ordovician magmatic arc, associated metamorphism and foreland basin formation characterized the Famatinian cycle. In Late Devonian, the collision of Chilenia and associated high-pressure/low-temperature metamorphism contrasts with the late Palaeozoic accretionary prisms. Contractional deformation in Early to Middle Permian was followed by extension and rhyolitic (Choiyoi) magmatism. Triassic to earliest Jurassic rifting was followed by subduction and extension, dominated by Pacific marine ingressions, during Jurassic and Early Cretaceous. The Late Cretaceous was characterized by uplift and exhumation of the Andean Cordillera. An Atlantic ingression occurred in latest Cretaceous. Cenozoic contraction and uplift pulses alternate with Oligocene extension. Late Cenozoic subduction was characterized by the Pampean flat-subduction, the clockwise block tectonic rotations in the normal subduction segments and the magmatism in Payenia. These processes provide evidence that the Andean tectonic model is far from a straightforward geological evolution.

The Andes make up the largest orogenic system developed by subduction of oceanic crust along a continental margin. Subduction began soon after the breakup of Rodinia in Late Proterozoic times, and since that time, it has been intermittently active up to the present. The evolution of the Pacific margin of South America during the Paleozoic occurred in the following stages: (1) initial Proterozoic rifting followed by subduction and final re-amalgamation of the margin in Early Cambrian times, as depicted by the Puncoviscana and Tucavaca Basins and related granitoids in southern Bolivia and northern Argentina; (2) a later phase of rifting in the Middle Cambrian, and subsequent collisions in Middle Ordovician times of parautochthonous terranes derived from Gondwana, such as Paracas, Arequipa, and Antofalla, and exotic terranes originating in Laurentia, such as Cuyania, Chilenia and Chibcha; (3) final Permian collision between South America and North America to form Pangea during the Alleghanides orogeny, leaving behind rifted pieces of Laurentia as the Tahami and Tahuin terranes in the Northern Andes and other poorly known orthogneisses in the Cordillera Real of Ecuador in the Late Permian–Early Triassic; and (4) amalgamation of the Mejillonia and Patagonia terranes in Early Permian times, representing the last convergence episodes recorded in the margin during the Gondwanides orogeny. These rifting episodes and subsequent collisions along the continental margin were the result of changes of the absolute motion of Gondwana related to global plate reorganizations during Proterozoic to Paleozoic times. Generalized rifting during Pangea breakup in the Triassic concentrated extension in the hanging wall of the sutures that amalgamated the Paleozoic terranes. The opening of the Indian Ocean in Early Jurassic times was associated with a new phase of subduction along the continental margin. The northeastward absolute motion of western Gondwana produced a negative trench roll-back velocity that controlled subduction under an extensional regime until late Early Cretaceous times. The Northern Andes of Venezuela, Colombia, and Ecuador record a series of collisions of island arcs and oceanic plateaus from the Early Cretaceous to the middle Miocene as a result of interaction with the Caribbean plate. The remaining Central and Southern Andes record periods of orogenesis and mountain building alternating with periods of quiescence and absence of deformation as recorded in parts of the Oligocene. Based on the generalized occurrence of flat-slab subduction episodes through time, as recorded in most of the Andean segments in Cenozoic and older times, this paper presents a conceptual orogenic cycle that accounts for the sequence of quiescence, minor arc magmatism, expansion and migration of the volcanic fronts, deformation, subsequent lithospheric and crustal delamination, and final foreland fold-and-thrust development. These episodes are related to shallowing and steepening of the subduction zones through time. This conceptual cycle, similar to the Laramide orogeny in North America, may be recognized wherever a subduction system is or was active in a continental margin.